1. Field of the Invention
This invention relates to lens systems having aspheric surfaces and a method for making such a lens system.
2. Description of the Prior Art
Because the use of aspheric surfaces improves optical performance of the lens system, the use of these surfaces is often a key to achieving the desired optical performance. This is especially true when the lens system has fewer lens elements--such as the lens system designed for use in single-use cameras. For example, U.S. Pat. Nos. 5,067,803 and 5,327,291 show the use of aspheric surfaces in such lens systems.
U.S. Pat. No. 5,067,803 discloses a two-element lens system for use in photographic cameras. This patent also uses two meniscus lens elements arranged around a central aperture stop. The disclosed lens system utilizes a single aspheric surface on either one or both of the lens elements.
U.S. Pat. No. 5,327,291 also discloses a two component objective lens system. The disclosed lens system utilizes a single aspheric surface on each of the two lens elements.
But, aspheric surfaces typically have a strong drawback when compared with spherical surfaces. That is, the lens components with aspheric surfaces are usually sensitive to decentering of the aspheric surface. When multiple aspheric surfaces are present in a lens system, tilts and/or decenterization of these aspheric surfaces with respect to one another and with respect to the rest of the lens system often introduces undesirable aberrations into the lens system and thus degrades the overall optical performance of the lens system. Therefore, lens components with aspheric surfaces often have to be assembled to very strict tolerances. This makes the lens assembly difficult and drives up the cost of the lens system.
It is advantageous for camera objectives (i.e., taking lenses) to have a wide-angle, fast lens system with a superior performance. Thus, notwithstanding the variety of objective lens systems which have been previously proposed, there still exists a need for lens systems with a plurality of aspheric surfaces which are not sensitive to aspheric decentering and which can be produced at low cost.
Applicant's invention addresses this need and represents a further improvement in lens systems having aspheric surfaces and especially in lens systems having biaspheric lens components.